The present invention relates to a metal laminate gasket for use in an internal combustion engine, and in particular to a metal laminate gasket which comprises bead portion(s) for surrounding hole(s) such as combustion chamber hole(s) to be sealed, and element(s) which is/are disposed in said bead portion(s) to serve as stopper(s) for limiting the degree of compression of the bead portion(s).
A cylinder head gasket comprises a single or a plural number of metal plates each having combustion chamber hole(s) and bolt holes, in which at least one of the metal plates having bead portion(s) for surrounding and sealing the combustion chamber hole(s). The bead portion has a projection formed on one surface of the metal plate and a recess formed on the other side of the projection on the other surface of the metal plate. The "bead portion" referred to in the present specification has such a meaning as mentioned above throughout the present specification.
U.S. Pat. Nos. 4,799,695 and 4,721,315 disclose the provision of stopper portions inside the bead portions (on the side of the combustion chamber holes), said stopper portions being formed by turning back the peripheries of the combustion chamber holes of the metal plates, or by laminating shim plates, so as to serve to limit the degree of compression of the bead portions. When the gaskets are compressed between the joint surfaces of cylinder heads and the joint surfaces of cylinder blocks, the above stopper portions serve to limit the degrees of compression of the bead portions, thereby limiting the amplitude of repetitive compression and restoration of the bead portions due to gas pressure in the combustion chambers. Thus, the gaskets are prevented from losing sealing effects because of less resilience of the bead portions due to their creep relaxation and because of the damages such as cracks during a long period of use.
Japanese Utility Model Laid-Open Publication No. 2-59361 discloses that a stopper portion for limiting the degree of compression of a bead portion is provided in the recess of the bead portion. The stopper portion, for example, consists of a shaped wire of mild steel fixed in the recess of the bead portion. Thus, cyclic loads applied to the bead portion while an engine is driven are absorbed by the clearance between the bottom face of the shaped wire and a surface to be sealed (i.e., by deformation of the bead portion) and deformation of the shaped wire. This publication also discloses a flame coating layer stopper as an alternative of the shaped wire stopper, said flame coating layer stopper being deformed by bolt-tightening and repetitive loads.
U.S. Pat. No. 4,140,323 discloses a resilient elastomeric sealant material to be disposed in the recess of a bead portion. The elastomeric sealant material disposed prevents the bead portions from flattening out, and thus concentrates the sealing effect on the zones of the bead portions, when a gasket is compressed between a pair of confronting surfaces to be sealed. The elastomeric sealant material also fills in scratches or other imperfections on the pair of the confronting surfaces to be sealed or the gasket surface, thereby preventing leakage from such imperfections.
The assignee of the present invention has proposed the following in Japanese Patent Application No. 8-38787 filed on Jan. 31, 1996 (Japanese Laid-Open Publication No. 9-210205): the recesses of the bead portions for surrounding holes to be sealed, of a metal gasket are partially filled with a non-compressible and non-deformable rigid synthetic resin such as an epoxy resin, wherein the height of the resin layers are lower at parts of the bead portions close to the bolt holes and it is higher at parts thereof spaced farther from the bolt holes. The rigid synthetic resin layers filling the parts of the recesses of the bead portions serve as stoppers for limiting the degree of compression of the bead portions, and they also serve to thicken the gasket at its portions filled with the resin layer more than the other portions to thereby enhance the sealing effect. Further, the height of the rigid synthetic resin layers are varied in accordance with the distance from the bolt holes, so that sealing pressure is equalized on the zones around holes to be sealed such as combustion chamber holes.
In a gasket in which the recesses of bead portions are filled with a resilient elastomer sealant, the elastomer sealant layers are deformed when the bead portions are compressed, so that irregular stresses are applied to the bead portions. When such stresses are applied to the bead portions repetitively, there is a fear that damages such as cracks may occur in the bead portions. In the meantime, the gasket with the recesses of the bead portions filled with the non-compressible and non-deformable rigid synthetic resin has not such a fear.
The metal gasket of the above application, however, has a problem that, when the gasket is compressed between a pair of the joint surfaces of a cylinder head and a cylinder block to allow the rigid synthetic resin layers to come into contact with one of the joint surfaces, the rigid synthetic resin layers are worn down because of friction with the joint surface due to vibrations of the joint surfaces during the operation of an engine or due to the thermal expansion or contraction of the joint surface accompanying the start or stop of the operation of the engine. Thus, during a long period of use, the function of the rigid synthetic resin layers as the stoppers are lost and the gasket thickness increasing effect by the rigid synthetic resin layers decreases, resulting in a fear of decreasing the sealing pressure.